Determination of morphine in human plasma by radioimmunoassay utilising a preliminary liquid-solid extraction

Numerous assays are available for the pharmacokinetic study of morphine. Two of these methods are compared with a new assay procedure, which involves a solid-phase extraction to clean up human plasma before radioimmunoassay allowing the determination of morphine levels to a sensitivity of 1 mugl(-1). Data are presented to show the importance of correct method choice if clinical studies are to be used in pharmacokinetic interpretations.